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Photosynthesis Summary Sheet (Higher levels 5 - 7)
Level 5 - Photosynthesis
Photosynthesis is a process where plants make glucose (sugar) to grow and respire. It requires water and
carbon dioxide, as well as sunlight and chlorophyll. It also produces oxygen as a waste product.
Photosynthesis is a chemical reaction and can be written as a word equation:
water
+
carbon dioxide
(+ light energy)  glucose (sugar) +
reactants
oxygen
products
Level 5 - Getting the water
Water is absorbed from the soil by the roots. Roots
are branched and spread out to help them absorb
water as possible.
They also have root hair cells which are adapted
to their function by having a large surface area to
help them absorb water quickly.
The water flows up hollow xylem tubes to the
leaf. Without water a plant would wilt and die.
Water is also needed because minerals are dissolved in it, which are needed to keep plants healthy.
The 3 main minerals needed are:
 Nitrates (N) for general growth
 Phosphates (P) for root growth
 Potassium (K) to stop the leaves turning yellow
Level 5 - Getting the carbon dioxide
Air, containing carbon dioxide, diffuses into
leaves through small holes called stomata.
Leaves are thin so that the carbon dioxide
does not need to go very far before reaching
the cells that need it.
Photosynthesis can often be speeded up by
increasing the amount of carbon dioxide
around a plant.
Level 5 - Getting the light
Many leaves are wide so that they have a big surface area to trap as much sunlight as possible. Most
photosynthesis happens in the palisade cells which are found near the upper surface of leaves. Palisade cells
are packed with chloroplasts. Chloroplasts contain chlorophyll (a green substance)
which absorbs light energy. Photosynthesis can often be speeded up by increasing the
amount of light.
chloroplasts
A palisade cell
Level 6 - Uses of glucose
Glucose is a type of sugar. It is used for three things:
• respiration
• making other substances that act as stores of energy (eg starch)
• making new materials for growth e.g. cellulose (for cell walls), fats (for cell membranes) and proteins
(for growth and seeds). New material is called biomass.
Level 6 - Respiration
Plant cells release the energy stored in glucose using respiration (another chemical reaction):
Glucose (sugar) + oxygen  carbon dioxide + water (+ energy)
Respiration happens all the time but photosynthesis can only happen when there is light.
Level 6 - Improving plant growth
When growing crop plants for food, farmers want to produce the largest amount of useful biomass (yield).
They use fertilisers to add minerals to the soil. Farmers can use manufactured (NPK) or natural organic
fertilisers to improve the quality of the soil.
Level 6 - Controlling environments to increase crop yields
The growth of crops in open fields is often affected by changes in the weather or season. Sometimes crops
are grown in carefully controlled conditions inside greenhouses.
Here the plants can be provided with:
- the optimum temperature
- light intensity
- carbon dioxide concentration
- supply of water
- supply of minerals
Level 7 - Maintaining a balance in the atmosphere
Plants absorb carbon dioxide and release oxygen when they do photosynthesis. They absorb oxygen and
release carbon dioxide when they use the glucose made to do respiration. These 2 processes happen at
different rates, which affects the concentration of each gas in the atmosphere.
oxygen
The plant does respiration all the time as it does not require light, so
the amount of oxygen (O2) absorbed for respiration is fairly constant.
The O2 levels only rise around the plant during daylight hours due to
the release of O2 by photosynthesis.
Carbon dioxide
Carbon dioxide and oxygen
levels around the plant
This graph shows the amount of carbon dioxide around an oak tree in
Summer. The Carbon dioxide (CO2) levels drop during the daylight
hours because it is absorbed when the plant does photosynthesis
(which needs light). There is more CO2 around the plant at night
because less is being absorbed.
Level 7 - Equations
You should be able to write the equations for photosynthesis as balanced symbol equations. Try to picture
these molecules using molymods or atom drawings.
sunlight
Photosynthesis
carbon dioxide + water

glucose
+ oxygen
chlorophyll
6CO2
Respiration
glucose
C6H12O6
+ 6H2O
+
+
oxygen
6O2

 carbon dioxide

6CO2
C6H12O6
+
6O2
+ water (+ energy)
+ 6H2O